The present invention relates to drill bit assemblies, specifically drill bit assemblies for use in subterranean drilling. More particularly the present invention relates to drill bits that include an inner bit. The prior art discloses drill bit assemblies comprising pilot bits.
One such pilot bit is disclosed in U.S. Pat. No. 7,207,398 to Runia et al., which is herein incorporated by reference for all that it contains. Runia et al. discloses a rotary drill bit assembly suitable for directionally drilling a borehole into an underground formation, the drill bit assembly having a bit body extending along a central longitudinal bit-body axis, and having a bit-body face at its front end, wherein an annular portion of the bit-body face is provided with one or more chip-making elements; a pilot bit extending along a central longitudinal pilot-bit axis, the pilot bit being partly arranged within the bit body and projecting out of the central portion of the bit-body face, the pilot bit having a pilot-bit face provided with one or more chip-making elements at its front end; a joint means arranged to pivotably connect the pilot bit to the bit body so that the bit-body axis and the pilot-bit axis can form a variable diversion angle; and a steering means arranged to pivot the pilot bit in order to steer the direction of drilling.
The prior art also teaches drill bit assemblies with shafts protruding from the working bit face. One such drill bit is disclosed in U.S. Pat. No. 7,360,610 to Hall et al, which is herein incorporated by reference for all that it contains. Hall et al. discloses a drill bit assembly which has a body portion intermediate a shank portion and a working portion, the working portion having at least one cutting element. A shaft is supported by the body portion and extends beyond the working portion. The shaft also has a distal end that is rotationally isolated from the body portion. The assembly comprises an actuator which is adapted to move the shaft independent of the body portion. The actuator may be adapted to move the shaft parallel, normal, or diagonally with respect to an axis of the body portion.